Is it safe to use approximate gather method to bake AO maps?
Having used Blender to bake AO myself, I can say that yes, it generally okay. Note that there will be a reduction in quality compared to a very high sample bake.
Approximate gather generally looks 'smoother' than low sample AO bakes but is less accurate. My advice would be to try both and compare inside your game.

So it mostly depends on your use case, but it should be ok.